Sildenafil Therapy For Subjects Who Derive Clinical Benefit From Continued Treatment With Sildenafil

Inclusion Criteria: * Patients Who Completed study A1481156 and Are Judged by the Investigator to Derive Clinical Benefit from Continued Treatment with Sildenafil, Prior to Reimbursement and Availability for Subjects in Russian Federation. * Child bearing age women should have appropriate contraception. * Signed informed consent. Patients who have a wish and possibility to follow treatment regimens in terms of the study. Exclusion Criteria: * Pregnant and lactating women. * Participation in other studies in the current moment or during study period except of A1481156. * Patients with severe acute or chronic diseases psychiatric disorders or laboratory abnormalities.